ML19203A309

LLC Supplemental Response to NRC Request for Additional Information No. 54 (Erai No. 8837) on the NuScale Design Certification Application

ML19203A309
Person / Time
Site:	NuScale
Issue date:	07/22/2019
From:	Rad Z NuScale
To:	Document Control Desk, Office of New Reactors
References
RAIO-0719-66379
Download: ML19203A309 (7)

Text

RAIO-0719-66379 July 22, 2019 Docket No.52-048 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk One White Flint North 11555 Rockville Pike Rockville, MD 20852-2738

SUBJECT:

NuScale Power, LLC Supplemental Response to NRC Request for Additional Information No. 54 (eRAI No. 8837) on the NuScale Design Certification Application

REFERENCES:

1. U.S. Nuclear Regulatory Commission, "Request for Additional Information No. 54 (eRAI No. 8837)," dated June 09, 2017

2. NuScale Power, LLC Response to NRC "Request for Additional Information No. 54 (eRAI No.8837)," dated August 03, 2017 The purpose of this letter is to provide the NuScale Power, LLC (NuScale) supplemental response to the referenced NRC Request for Additional Information (RAI).

The Enclosure to this letter contains NuScale's supplemental response to the following RAI Question from NRC eRAI No. 8837:

03.11-6 This letter and the enclosed response make no new regulatory commitments and no revisions to any existing regulatory commitments.

If you have any questions on this response, please contact Carrie Fosaaen at 541-452-7126 or at cfosaaen@nuscalepower.com.

Sincerely, Zackary W. Rad Director, Regulatory Affairs NuScale Power, LLC Distribution: Gregory Cranston, NRC, OWFN-8H12 Samuel Lee, NRC, OWFN-8H12 Marieliz Vera, NRC, OWFN-8H12 : NuScale Supplemental Response to NRC Request for Additional Information eRAI No. 8837 NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvalis, Oregon 97330, Office: 541.360.0500, Fax: 541.207.3928 www.nuscalepower.com

RAIO-0719-66379 :

NuScale Supplemental Response to NRC Request for Additional Information eRAI No. 8837 NuScale Power, LLC 1100 NE Circle Blvd., Suite 200 Corvalis, Oregon 97330, Office: 541.360.0500, Fax: 541.207.3928 www.nuscalepower.com

Response to Request for Additional Information Docket No.52-048 eRAI No.: 8837 Date of RAI Issue: 06/08/2017 NRC Question No.: 03.11-6 Regulatory Basis 10 CFR 50.49 and 10 CFR Part 50, Appendix A, Criterion 4 require that certain components important to safety be designed to withstand environmental conditions, including the effects of radiation, associated with design basis events, including normal operation, anticipated operational occurrences, and design basis accidents.

DSRS Section 3.11 indicates that the applicants safety analysis report should be sufficient to support the conclusion that all equipment that are important to safety are capable of performing their design safety functions under all environmental conditions that may result from any normal mode of plant operation, anticipated operational occurrence, design basis events, and post-design basis events.

DSRS Section 3.11 also states that the staff will conclude that the environmental design and qualification of mechanical, electrical, and I&C equipment that are important to safety are acceptable and meet applicable regulations, based on the finding that the applicant has implemented an environmental design and qualification program that provides adequate assurance that mechanical, electrical, and I&C equipment that are important to safety will function as intended in the event of anticipated operational occurrences, as well as in the normal, accident, and post-accident environmental conditions. The applicant's environmental design and qualification program should be in accordance with the requirements and guidance described in the regulations, regulatory guides and industry standards identified in Subsection II of DSRS Section 3.11.

Finally, RGs 1.89 and 1.183 provide guidance on how to perform the radiological analysis related to equipment qualification. These guides indicate that assuming 1% failed fuel cladding NuScale Nonproprietary

or the technical specification primary coolant activity limits, would be an acceptable assumption to use in calculating the normal operation equipment qualification dose.

Question DCD Section 3C.4.3, under Radiation Dose Effects, states, In general, dose rate effects occur over long periods and, therefore, need only be addressed during the radiation conditions that occur during normal plant operation.

a. This statement appears inconsistent with other information in the DCD which indicates that both normal operation and accident conditions are considered. For example, DCD Section 3C.5.4, under Design Basis Event Radiation Doses states, The required dose used for environmental qualification considers the total integrated dose consisting of the normal dose plus the accident dose corresponding to the required post- accident operating time. The normal dose considers gamma and neutron effects, while the accident dose considers the gamma and beta dose that is expected at the equipment location. Please explain how accident conditions have been considered and ensure that the DCD is consistent.

b. If accident conditions have been categorically excluded, please provide additional technical justification for excluding their consideration.

c. In addition, please describe any situations when the dose rate received during accident conditions has been or needs to be included.

NuScale Response:

The following is provided as a change to the RAI response for question 3.11-6 provided to the NRC. During discussions with the NRC, the staff requested that the language of the previous RAI response and the FSAR be clarified related to the synergistic dose rate effects.

"The discussion in FSAR Appendix 3C.4.3, under Radiation Dose Effects, is specifically dealing with synergistic effects related to radiation dose rate effects. This section of the NuScale Nonproprietary

FSAR is intended to describe how the NuScale EQ program addresses, or otherwise accounts for known synergistic effects, as required by 10 CFR 50.49 and RG 1.89, Revision 1. The statement that In general, dose rate effects occur over long periods and, therefore, need only be addressed during the radiation conditions that occur during normal plant operation. reflects the need to consider the potential for lower dose rates during normal operation to produce more severe degradation for certain materials compared to higher dose rates used to accelerate the radiation exposure time during a qualification test program. This should not be considered to be inconsistent or in conflict with other sections of the FSAR which describe how qualification to the total integrated (normal + accident) dose will be conducted.

FSAR Appendix 3C.5.4, Design Basis Event Radiation Doses clearly specifies that the required dose used for environmental qualification considers the total integrated dose consisting of the normal dose plus the accident dose corresponding to the required post-accident operating time. The normal dose considers gamma and neutron effects, while the accident dose considers the gamma and beta doses that are postulated at the equipments location.

The qualification to the postulated radiation environment is based on the total dose expected during normal operation over the installed life of the equipment, and the radiation environment associated with the most severe design basis accident during for which the equipment is required to function and is consistent with 10 CFR 50.49 e(4).

The only consideration of the dose rate effects involves dose rate synergistic effects under normal operating conditions as described in FSAR Appendix 3C.4.3.

As addressed in the original NuScale response to RAI Question 3.11-6, consideration is given to the potential for lower dose rates during normal operation to produce more serve degradation for certain materials compared to higher dose rates used to accelerate the radiation exposure time during a qualification test program. The last sentence of FSAR Section 3C.4.3 was determined to be confusing and not necessary, therefore it was deleted.

The following change to the FSAR 3C.4.3 Radiation Dose Effects has been incorporated:

"The need for qualification due to radiation exposure is evaluated for each piece of equipment. The radiation environment is based on the type of radiation, the total dose expected during normal operation over the installed life of the equipment, and the radiation environment associated with the most severe design basis accident during or following which the equipment is required to remain functional.

NuScale Nonproprietary

In general, dose rate effects occur over long periods and, therefore, need only be addressed during the radiation conditions that occur during normal plant operation."

Impact on DCA:

FSAR Section 3C.4.3 has been revised as described in the response above and as shown in the markup provided in this response.

NuScale Nonproprietary

Methodology for Environmental Qualification of Electrical and NuScale Final Safety Analysis Report Mechanical Equipment interaction effects are minute by comparison to the primary effects, and thus require significantly more experimental evidence to identify. Current research, as referenced below, indicates that synergistic effects can typically be categorized under two main headings:

• Test sequence effects - The sequence in which radiation and thermal aging exposures occur is an important consideration. Radiation combined with elevated temperatures or radiation followed by elevated temperatures may produce more material degradation than when thermal aging precedes radiation exposure (NUREG/CR-3629 (Reference 3C-14)).

• Radiation dose rate effects - For many materials, it has been observed that lower dose rates produce more degradation than a higher dose rate for the same total applied dose (NUREG/CR-2157 (Reference 3C-15)).

Test Sequence Effects An important aging consideration is the possible existence of synergistic effects when multiple stress environments such as radiation and elevated temperatures, are applied simultaneously. Currently, sequential exposure is the only commercially available means of testing; no commercial facility offers simultaneous steam and radiation exposure. Although sequential and simultaneous tests can produce variances in degradation, the differences tend to be minor compared to total degradation. The possibility that significant synergistic effects may exist is addressed by the using the "worst-case" aging sequence, conservative accelerated aging parameters and conservative, DBE test levels to provide confidence that any synergistic effects are enveloped.

Radiation Dose Effects The need for qualification due to radiation exposure is evaluated for each piece of equipment. The radiation environment is based on the type of radiation, the total dose expected during normal operation over the installed life of the equipment, and the radiation environment associated with the most severe design basis accident during or following which the equipment is required to remain functional.

RAI 03.11-6S1 In general, dose rate effects occur over long periods and, therefore, need only be addressed during the radiation conditions that occur during normal plant operation.

3C.4.4 Operating Time RAI 03.11-7 Equipment required to be environmentally qualified has one or more of the following design functions related to safety: reactivity control, decay heat removal, post-accident monitoring, containment isolation, maintenance of RCS pressure boundary integrity, control room habitability, event severity mitigation or system support functions. For each function, a period of operability is assigned that ranges from less than 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> to a maximum of 2400 hours0.0278 days <br />0.667 hours <br />0.00397 weeks <br />9.132e-4 months <br />. The assignment of these post accident operating times is Tier 2 3C-8 Draft Revision 3